The subject matter disclosed herein relates generally to industrial control networks for controlling machines and industrial processes and, more specifically, to an output module receiving data from other nodes in the network and providing signals to control actuators or other devices on the machine or process.
Industrial controllers are special purpose computers used for controlling factory automation and the like. Industrial controllers typically execute a control program highly customized to a particular control application. Special control languages, such as “relay ladder logic” are normally used to facilitate programming of the device. Under the direction of the stored program, a processor of the industrial controller periodically examines the state of input devices and updates the state of output devices. In order to ensure predictable control of a machine or process, the control program must be highly reliable and deterministic, that is, executing at well-defined time periods.
As industrial processes grow in complexity, an increasing number of devices are being connected to the industrial controller. The devices are often distributed about a machine or along a process line. The increasing number of devices and distribution of these devices about the machine require more complex control programs. Thus, it would be desirable to provide output modules that are configured to simplify setup and commissioning, thereby reducing the time and expense involved in developing the industrial control system.
An industrial network is typically used to connect the distributed devices and to allow data to be transmitted between the devices. However, the increasing number of devices requires an increased volume of communications between those devices. Further, various scan rates on the controller and remote modules as well as transmission delays between devices introduce further challenges to maintain the high reliability and deterministic nature of the control programs. Thus, it would be desirable to provide output modules that are configured to reduce the delay times in communications between devices in order to maintain the high reliability and deterministic nature of the control programs.
It may be desirable to generate a pulse width modulated (PWM) signal at one or more of the output terminals. The PWM signal alternates between an on state and an off state during a defined time period. The duration at which the output is in the on state may be varied within the time period to vary a commanded magnitude between zero and one hundred percent. Alternately, the PWM signal may be output at a fixed duration, such as a 50% duty cycle, in response to an input signal. Thus, the PWM output signal may be used to vary the duty cycle of a controlled process or to initiate a repeated process in response to a desired initial condition being detected at an input.
However, generating a PWM output signal has not been met without certain limitations. Providing the PWM output signal has required the end user to create a program executing on the processor. Further, the processor monitors the input signals, transmitted via a network from a remote location, processes the inputs, and generates a PWM output signal. The PWM output signal typically requires a fixed time period. Transmission, scanning, and processing delays, may result in either additional pulses being generated or desired pulses being dropped in response to input signals. If multiple PWM output signals exist on the same output module, they are turned on at the start of the period and remain on for their respective desired percentage of the period, or duty cycle. However, turning on each of the outputs at the same time results in maximum loading of the output module. Thus, it would be desirable to provide an output module that generates a PWM output signal, addressing the aforementioned limitations.